1. Field of the Invention
This invention relates to squarylium dyes, and processes and intermediates for the preparation thereof. More specifically, it relates to such dyes and intermediates in which the squarylium ring bears an amino or substituted amino group, and also certain other intermediates useful for the preparation of the aforementioned dyes.
2. References to Related Applications
U.S. Pat. No. 5,405,976 and International Application No. PCT/US91/08695 (Publication No. WO 92/09661) describe dyes comprising an inner salt of a compound of the formula: EQU Q.sup.1 =Z-Z.sup.2
wherein:
Q.sup.1 is a 4-(benz[b]-4H-pyrylium)methylidene, 4-(benz[b]-4H-thiopyrylium)methylidene or 4-(benz[b]-4H-selenopyrylium)methylidene grouping;
Z is a 1,3-(2-hydroxy-4-oxo-2-cyclobutylidene) or 1,3-(2-hydroxy-4,5-dioxo-2-cyclopentylidene) ring; and
Q.sup.2 is a 4-(benz[b]-4H-pyran-4-ylidene)methyl, 4-(benz[b]-4H-thiopyran-4-ylidene)methyl or 4-(benz[b]-4H-selenopyran-4-ylidene)methyl grouping;
wherein at least one of the groupings Q.sup.1 and Q.sup.2 carries at its 2-position a substituent in which a non-aromatic carbon atom is bonded directly to the benzpyrylium, benzthiopyrylium or benzselenopyrylium nucleus, subject to the proviso that if this 2-substituent contains an aromatic nucleus, this aromatic nucleus is not conjugated with the benzpyrylium, benzthiopyrylium or benzselenopyrylium nucleus to which it is attached. These dyes have high absorptions in the near infra-red, and improved solubility in semi-polar solvents and plastics. The dyes disclosed in these applications include certain infra-red dyes which can be used in the thermal imaging medium described below with reference to FIG. 6.
Copending application U.S. Ser. No. 07/696,222, filed May 6, 1991 (now U.S. Pat. No. 5,231,190) and assigned to the same assignee as the present application, and the corresponding European Application No. 92107574.3, describe and claim the squarylium compounds of formulae D, E, J and K described below with reference to FIG. 1, together with similar compounds containing different heterocyclic nuclei, and squarylium compounds of the formula: ##STR2## wherein Q.sup.1 and Q.sup.2 are each independently a heterocyclic nucleus such that in the compounds of formulae Q.sup.1 CH.sub.2 R.sup.1 and Q.sup.2 CH.sub.2 R.sup.2 the methylene hydrogens are active hydrogens, the atoms of Q.sup.1 and Q.sup.2 which are bonded directly to the CR.sup.1 and CR.sup.2 groupings respectively each being part of an aromatic ring, and Q.sup.1 and Q.sup.2 are different, and R.sup.1 and R.sup.2 are each independently a hydrogen atom or an aliphatic or cycloaliphatic group. The disclosure of this copending U.S. application is discussed below in more detail with reference to FIG. 1.
Copending applications U.S. Ser. Nos. 07/695,641 (now U.S. Pat. No. 5,342,816) 07/696,196 (see also the corresponding European Application No. 92107576.8 (Publication No. 512,476)) and 07/695,932 (now U.S. Pat. No. 5,153,169, issued Oct. 6, 1992), all filed May 6, 1991 and all assigned to the same assignee as the present application, describe and claim imaging media comprising a color-forming layer comprising a thermal color-forming composition adapted to undergo a change of color upon increase in the temperature of the color-forming layer above a color-forming temperature for a color-forming time. Preferred imaging media described in these three applications comprise three separate color-forming layers containing yellow, cyan and magenta thermal color-forming compositions; each of these color-forming compositions comprises a color-forming compound which undergoes a change of color upon healing above the color-forming temperature for the color-forming time, and an infra-red absorber capable of absorbing infra-red radiation and thereby generating heat in the color-forming layer. The three color-forming layers use infra-red absorbers absorbing at differing wavelengths so that each color-forming layer can be imaged independently; for example, specific imaging media disclosed in these three applications use infra-red absorbers having peak absorptions at approximately 792, 822 and 869 nm.
Copending application U.S. Ser. No. 07/795,341, filed Nov. 20, 1991 (now U.S. Pat. No. 5,206,206), and assigned to the same assignee as the present application, describes infra-red dyes generally similar to those of the present invention, but in which the 2-substituent on the squarylium ring has a carbon atom directly bonded to the squarylium ring.
Copending application U.S. Ser. No. 07/795,101, filed Nov. 20, 1991 and assigned to the same assignee as the present application describes and claims thermal imaging media generally similar to those described in the aforementioned applications U.S. Ser. Nos. 07/695,641; 07/696,196 and 07/695,932 but in which at least one imaging layer contains a metal cation. Preferred imaging media described in this application have imaging layers containing zinc acetate, as described below with reference to FIG. 6.
The disclosures of all the aforementioned copending U.S. applications and patents are herein incorporated by reference.
3. Description of the Prior Art
It is known that compounds in which two chromophoric groups are linked by a pentamethine chain, the three central carbon atoms of which form part of a squarylium ring are useful as dyes, especially near infra-red dyes. (The term "near infra-red" is used herein to mean electromagnetic radiation having a wavelength of about 700 to about 1200 nm.)
The term "chromophoric group" is used herein to mean a group containing a plurality of conjugated unsaturated linkages arranged so that the unsaturated linkages are conjugated with the squarylium ring via the unsaturated (sp.sup.2) meso carbon atom lying between the chromophoric group and the squarylium ring, the chromophoric group being such that the squarylium dye has substantial absorption of visible or infra-red radiation.
For example, Japanese Patent Application No. 103,604/82 (Publication No. 220,143/83, published Dec. 21, 1983), discloses a broad class of bis-heterocyclic pentamethine dyes in which the central three carbon atoms of the pentamethine chain form part of a squarylium or croconylium ring. The heterocyclic nuclei can be pyrylium, thiopyrylium, selenopyrylium, benzpyrylium, benzthiopyrylium, benzselenopyrylium, naphthopyrylium, naphthothiopyrylium or naphthoselenopyrylium nuclei, which can be substituted with alkyl, alkoxy, aryl or styryl groups.
Japanese Patent Application No. 60-8730 (Publication No. 167,681/86, published Jul. 29, 1986), discloses bis(4-benz[b]thiopyrylium) pentamethine dyes in which the central three carbon atoms of the pentamethine chain form part of a squarylium ring. The dyes are intended for use as infra-red absorbers.
U.S. Pat. No. 4,508,811, issued Apr. 2, 1985, describes an optical recording element in which the recording layer comprises a bis(2,6-dialkyl)-pyrylium or -thiopyrylium squarylium salt.
The squarylium dyes disclosed in these Japanese applications and U.S. patent are capable of achieving high extinction coefficients in the near infra-red range. However, such squarylium dyes suffer from a number of disadvantages. Many of these prior art dyes have low solubility in most plastics and/or in semi-polar solvents (for example, methyl ethyl ketone and methylene chloride) from which they need to be deposited to form imaging media. Thus, it is difficult to dissolve or disperse the absorber in a plastic without forming large aggregates and without adversely affecting other properties of the plastic.
A related disadvantage is that, unless specific functional groups are provided on the chromophoric groups (and the presence of such functional groups on the chromophoric groups may cause problems in the synthesis of the compounds from which the chromophoric groups are derived, or in the condensation of these compounds with squaric acid or its derivatives to form the final dyes), there is no convenient site (or "handle") on the squarylium dye for attachment of functional groups. Attachment of functional groups to the squarylium ring may be desirable, for example, to change the solubility of the dye in, or its compatibility with, various media, or to permit the dye to be chemically bonded to other materials.
Thirdly, among the squarylium dyes disclosed in these Japanese applications and U.S. patent, it may be difficult to find a dye which absorbs at the precise wavelength required for a particular application. For example, when choosing infra-red absorbers for use in imaging media such as those described in the aforementioned applications U.S. Ser. Nos. 07/695,641; 07/696,196 and 07/695,932, the need for independent addressing of the three color-forming layers, coupled with the widths of the peaks (typically the full-width-half-maximum (FWHM) of these peaks is about 35-40 nm) and the limited wavelength range over which present semiconductor lasers can be produced economically, mean that it is often necessary to find an infra-red absorber which has an absorption peak within a very narrow range (say 10-15 nm) and which meets all the other requirements of stability, solubility and compatibility with other components of the imaging medium required for use in such an imaging medium. It is often difficult if not impossible to find a squarylium dye from among those disclosed in the Japanese applications and U.S. patent which absorbs within such a narrow wavelength range.
The aforementioned disadvantages of earlier prior art squarylium dyes are greatly reduced in the dyes described in the aforementioned applications U.S. Ser. Nos. 07/616,639, 07/795,038 and 07/696,222. The 2-non-aromatic substituted dyes described in applications U.S. Ser. Nos. 07/616,639 and 07/795,038 are substantially more soluble than the corresponding 2-phenyl dyes, while the asymmetric dyes which can be synthesized in good yields by the processes described in application U.S. Ser. No. 07/696,222 greatly ease the task of finding a dye which absorbs at a desired wavelength, since the ability to change the two chromophoric groups independently gives an additional degree of freedom, as compared with earlier dyes in which the two chromophoric groups were the same. However, neither of these copending applications describes dyes in which functional groups are provided on the squarylium ring itself. Furthermore, there are still situations in which it would be advantageous to provide dyes with even greater solubility in certain media than those described in applications U.S. Ser. Nos. 07/616,639 and 07/795,038, and it would also be advantageous to provide some way in which the dyes disclosed in applications U.S. Ser. Nos. 07/616,639, 07/795,038 and 07/696,222 could be "fine tuned" by shifting their infra-red absorption peaks over small ranges (say 30 nm) in order to assist in providing dyes having absorptions within very narrow desired ranges.
It has now been found that providing an amino or substituted amino group in place of one of the oxygen atoms of the squarylium ring in squarylium dyes (the resulting dye being hereinafter referred to as an "aminosquarylium" dye) allows the absorption peak of the dye to be shifted somewhat, allows various functional groups to be incorporated conveniently into the dye, and may increase the solubility of the dye in, or its compatibility with, certain media. The amino group on the squarylium ring also provides a potential means for chemically bonding the dye to other materials. Accordingly, this invention is directed to these aminosquarylium dyes, to processes and intermediates for the preparation of such dyes, and to processes and imaging media containing these dyes.